Method for block polymer synthesis by controlled radical polymerisation

ABSTRACT

The invention relates to a process for polymerizing block polymers of general formula (I): ##STR1## in which process the following are brought into contact with each other: an ethylenically unsaturated monomer of formula: 
     
         CYY&#39;(═CW--CW&#39;).sub.a ═CH.sub.2, 
    
     a precursor compoun of general formula (II): ##STR2## a radical polymerization initiator.

This application is an application under 35 U.S.C. Section 371 ofInternational Application Number PCT/FR98/01316, filed on Jun. 23, 1998.

The present invention relates to a novel radical polymerization processfor obtaining block copolymers.

Block polymers are usually prepared by ionic polymerization. This typeof polymerization has the drawback of only allowing the polymerizationof certain types of non-polar monomers, especially styrene andbutadiene, and of requiring a particularly pure reaction mixture andtemperatures which are often below room temperature so as to minimizeparasitic reactions, and hence of severe operational constraints.

Radical polymerization has the advantage of being easily carried outwithout having to comply with excessive purity conditions, and attemperatures greater than or equal to room temperature. However, untilrecently a radical polymerization process allowing block polymers to beobtained did not exist.

Since then, a new radical polymerization process has been developed,namely "controlled" or "living" radical polymerization. Controlledradical polymerization takes place by the growth, by propagation, ofmacroradicals. These macroradicals, which have a very short lifetime,recombine irreversibly by coupling or dismutation. When thepolymerization takes place in the presence of several comonomers, thecompositional variation of the mixture is infinitely slow compared withthe lifetime of the macroradical so that the chains have a sequence ofrandom monomer units and not a block-type sequence.

Recently, controlled radical polymerization techniques have beendeveloped in which the ends of polymer chains may be reactivated in theform of a radical by homolytic bond (for example, C--O or C-halogen)scission.

Controlled radical polymerization therefore has the following distinctcharacteristics:

1. the number of chains is fixed throughout the duration of thereaction,

2. the chains all grow at the same rate, resulting in:

a linear increase in the molecular masses with conversion,

a narrow distribution of masses,

3. the average molecular mass is controlled by themonomer/chain-precursor molar ratio, and

4. the possibility of preparing block copolymers.

The controlled character is even more pronounced when the rate ofreactivation of the chains into radicals is very much greater than therate of growth of the chains (propagation). There are cases where thisis not always true (i.e. the rate of reactivation of the chains intoradicals is greater than or equal to the propagation rate) andconditions 1 and 2 are not observed, nevertheless it is always possibleto prepare block copolymers.

Several approaches have been described for controlling radicalpolymerization. The most commonly cited consists in introducing, intothe mixture, counter radicals which combine reversibly with the growingmacroradicals, such as, for example, nitroxyl radicals (Georges et al.,Macromolecules, 26, 2987, (1993)). This technique is characterized byhigh temperatures for labilizing the C--O bond.

Another method, called Atom Transfer Radical Polymerization, makes useof transition metal salts combined with organic ligands and an initiatorgenerally consisting of an organic halide; control of the polymerizationis made possible by the reversibility of the C-halogen bond (K.Matyjaszewski, PCT WO 96/30421). One drawback with this polymerizationis that a stoichiometric quantity of metal per chain remains.

Otsu (Otsu et al., Makromol. Chem. Rapid Comm., 3, 127-132, (1982), Otsuet al. ibid, 3, 123-140, (1982), Otsu et al., Polymer Bull., 7, 45,(1984), ibid, 11, 135, (1984), Otsu et al, J. Macromol. Sci. Chem., A21,961, (1984) and Otsu et al., Macromolecules, 19, 2087, (1989)) has shownthat certain organic sulphides, particularly dithiocarbamates, allowedchains to be grown in a controlled manner under UV irradiation,according to the principle: ##STR3##

The principle relies on the photolysis of the C--S bond, whichregenerates the carbon macroradical, on the one hand, and thedithiocarbamyl radical, on the other hand. The controlled character ofthe reaction is due to the reversibility of the C--S bond under UVirradiation. It is thus possible to obtain block copolymers. On theother hand, the equilibrium constant of reaction 1 above is not verylarge compared with the rate of propagation, this having the consequenceof generating relatively broad molecular mass distributions. Thus, thedispersion index (DI=M_(w) /M_(n)) is between 2 and 5 (Otsu et al., 25,7/8, 643-650, (1989)).

Xanthate disulphides and dithiocarbamate disulphides are themselves wellknown as transfer agents in conventional radical polymerization inthermal mode and in the presence of an initiator, but no one hashitherto been able to control the polymerization, or even less toproduce block copolymers.

Up till now it was known that disulphides (tetraalkylthiuram disulphide,diisopropylxanthate disulphide and mercaptobenzothiazol disulphide) wereactivatable thermally or under UV irradiation, whereas monosulphides(substituted xanthates, dithiocarbamates) were activatable only under UVirradiation (Roha et al., Macromol. Symp., 91, 81-92, (1995), andOkawara et al., Bull. of the Tokyo Inst. of Techn., No. 78, 1966).

However, controlled radical polymerization making use of a UVirradiation source is very difficult to carry out, especially from anindustrial standpoint, since the penetration of the UV photons into thepolymerization medium is limited, both by absorption phenomena (most ofthe ethylenic monomers absorb in the 210-280 nm range) and by diffusionphenomena in disperse media (suspension, emulsion).

Moreover, it has been shown (Turner et al., Macromolecules, 23,1856-1859, (1990)) that photopolymerization in the presence ofdithiocarbamate generates carbon disulphide and may be accompanied by aloss of polymerization control.

For these reasons, it has thus been sought to develop a technique whichcan be used to obtain block copolymers by a process without UVirradiation, preferably by thermal initiation.

Until the present time, no controlled radical polymerization system hasbeen able to be demonstrated using dithio compounds in the absence of aUV source.

Controlled radical polymerization has an advantage over conventionalradical polymerization when it is a question of preparinglow-molecular-weight functionalized chains (reactive telomers). Suchpolymers are desirable for specific applications such as, for example,coatings and adhesives.

Thus, when it is attempted to synthesize chains grafted with, onaverage, 2 functional comonomers, the fraction of chains with at mostone functional site becomes large when the average degree ofpolymerization is less than a threshold value (e.g. 20 or 30).Controlled radical polymerization makes it possible to reduce, or evento inhibit, the formation of these oligomers having zero or onefunctional site which degrade the performance in terms of application.

One object of the present invention is to provide a novel controlledradical polymerization process for the synthesis of block polymers.

Another object of the present invention is to provide a controlledradical polymerization process for the synthesis of block polymers inthe absence of a UV source.

Another object is to provide a controlled radical polymerization processfor the synthesis of block polymers from all types of monomers.

Another object is to provide a controlled radical polymerization processfor the synthesis of block polymers containing no metal impuritiesdeleterious to their use.

Another object is to provide a controlled radical polymerization processfor the synthesis of block copolymers, the said polymers being chain-endfunctionalized.

Another object is to provide a controlled radical polymerization processfor the synthesis of block polymers and block copolymers having a lowpolydispersity index.

Another object is to provide a controlled radical polymerization processfor the synthesis of oligomers in which the number of functional unitsis constant from chain to chain.

To this end, the invention relates to a process for polymerizing blockpolymers of general formula (I): ##STR4## in which process, thefollowing are brought into contact with each other: an ethylenicallyunsaturated monomer of formula:

    CYY'(═CW--CW').sub.a ═CH.sub.2,

a precursor compound of general formula (II): ##STR5## a radicalpolymerization initiator.

The invention also relates to the block polymers which can be obtainedby the above process.

Finally, the invention relates to polymers of general formula (II), thepolydispersity index of which is at most 2.

Further details and advantages of the invention will appear more clearlyon reading the description and the examples.

The invention therefore relates first of all to a process forpolymerizing block polymers of general formula (I): ##STR6## in which:Z¹ =S or P,

Z² =O, S or P,

R¹ and R², which are identical or different, represent:

an optionally substituted alkyl, acyl, aryl, alkene or alkyne group (i),or

an optionally substituted, saturated or unsaturated, carbon-containingor aromatic ring (ii), or

an optionally substituted, saturated or unsaturated heterocycle (iii),

it being possible for these groups and rings (i), (ii) and (iii) to besubstituted with substituted phenyl groups, substituted aromatic groups,or groups: alkoxycarbonyl or aryloxycarbonyl (--COOR), carboxy (--COOH),acyloxy (--O₂ CR), carbamoyl (--CONR₂), cyano (--CN), alkylcarbonyl,alkylarylcarbonyl, arylcarbonyl, arylalkylcarbonyl, phthalimido,maleimido, succinimido, amidino, guanidimo, hydroxyl (--OH), amino(--NR₂), halogen, allyl, epoxy, alkoxy (--OR), S-alkyl, S-aryl, groupshaving a hydrophilic or ionic character, such as the alkali metal saltsof carboxylic acids, the alkali metal salts of sulphonic acid,polyalkylene oxide chains (PEO, PPO), cationic substituents (quaternaryammonium salts), R representing an alkyl or aryl group,

a polymer chain,

V, V', W and W', which are identical or different, represent: H, analkyl group or a halogen,

X, X', Y and Y', which are identical or different, represent H, ahalogen or an R³, OR³, OCOR³, NHCOH, OH, NH₂, NHR³, N(R³)₂, (R³)₂ N⁺ O⁻,NHCOR³, CO₂ H, CO₂ R³, CN, CONH₂, CONHR³ or CONR³ ₂ group, in which R³is chosen from alkyl, aryl, aralkyl, alkaryl, alkene or organosilylgroups, optionally perfluorinated and optionally substituted with one ormore carboxyl, epoxy, hydroxyl, alkoxy, amino, halogen or sulphonicgroups,

a and b, which are identical or different, are equal to 0 or 1,

m and n, which are identical or different, are greater than or equal to1 and, when one or other is greater than 1, the individual repeat unitsare identical or different,

in which process the following are brought into contact with each other:

an ethylenically unsaturated monomer of formula:

    CYY'(═CW--CW').sub.a ═CH.sub.2,

a precursor compound of general formula (II): ##STR7## a radicalpolymerization initiator.

The process therefore consists in bringing into contact with each othera radical polymerization initiator, an ethylenically unsaturated monomerand a precursor of general formula (II).

The radical polymerization initiator may be chosen from the initiatorsconventionally used in radical polymerization. These may, for example,be one of the following initiators:

hydrogen peroxides such as: tert-butyl hydroperoxide, cumenehydroperoxide, tert-butyl peroxyacetate, tert-butyl peroxybenzoate,tert-butyl peroxyoctoate, tert-butyl peroxyneodecanoate, tert-butylperoxyisobutyrate, lauroyl peroxide, tert-amyl peroxypivalate,tert-butyl peroxypivalate, dicumyl peroxide, benzoyl peroxide, potassiumpersulphate and ammonium persulphate;

azo compounds such as: 2-2'-azobis(isobutyronitrile),2,2'-azobis(2-butanenitrile), 4,4'-azobis(4-pentanoic acid),1,1'-azobis(cyclohexanecarbonitrile), 2-(tert-butylazo)-2-cyanopropane,2,2'-azobis[2-methyl-N-(1,1)-bis(hydroxymethyl)-2-hydroxyethyl]propionamide,2,2'-azobis(2-methyl-N-hydroxyethyl)propionamide,2-2'-azobis(N,N'-dimethyleneisobutyramidine)dichloride,2,2'-azobis(2-amidinopropane)dichloride,2,2'-azobis(N,N'-dimethyleneisobutyramide),2,2'-azobis(2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]propionamide),2,2'-azobis(2-methyl-N-[1,1-bis(hydroxymethyl)ethyl]propionamide),2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide] and2,2'-azobis(isobutyramide)dihydrate;

redox systems including combinations such as:

mixtures of hydrogen peroxide or alkyl peroxide, peresters,percarbonates and the like and of any one of the salts of iron, titanoussalts, zinc formaldehyde sulphoxylate or sodium formaldehydesulphoxylate, and reducing sugars;

alkali-metal or ammonium persulphates, perborates or perchlorates incombination with an alkali metal bisulphite, such as sodiummetabisulphite, and reducing sugars;

alkali-metal persulphates in combination with an arylphosphinic acid,such as benzenephosphonic acid and other similar acids, and reducingsugars.

The amount of initiator to be used is determined so that the amount ofradicals generated is at most 20 mol % with respect to the amount ofcompound (II), preferably at most 5 mol %.

As ethylenically unsaturated monomer, the monomers chosen from styreneor its derivatives, butadiene, chloroprene, (meth)acrylic esters, vinylesters and vinyl nitriles are more specifically used according to theinvention.

Butadiene and chloroprene correspond to the case in which a and b=1 inthe formulae (I), (II) and in the formula for the monomer given above.

"(Meth)acrylic esters" should be understood to mean esters of acrylicacid and of methacrylic acid with hydrogenated or fluorinated C₁ -C₁₂,preferably C₁ -C₈, alcohols. Among compounds of this type, mention maybe made of: methyl acrylate, ethyl acrylate, propyl acrylate, n-butylacrylate, isobutyl acrylate, 2-ethylhexyl acrylate, tert-butyl acrylate,methyl methacrylate, ethyl methacrylate, n-butyl methacrylate andisobutyl methacrylate.

The vinyl nitriles include more particularly those having from 3 to 12carbon atoms, such as, in particular, acrylonitrile andmethacrylonitrile.

It should be noted that styrene may be replaced, completely or partly,by derivatives such as alpha-methylstyrene or vinyltoluene.

The other ethylenically unsaturated monomers which can be used, alone oras mixtures, or which can be copolymerized with the above monomers, are,for example:

vinyl esters of carboxylic acids, such as vinyl acetate, vinyl versatateand vinyl propionate;

vinyl halides;

ethylenically unsaturated monocarboxylic and dicarboxylic acids, such asacrylic acid, methacrylic acid, itaconic acid, maleic acid and fumaricacid, and monoalkyl esters of dicarboxylic acids of the type mentionedwith alkanols preferably having from 1 to 4 carbon atoms and theirN-substituted derivatives;

amides of unsaturated carboxylic acids, such as acrylamide,methacrylamide, N-methylolacrylamide or methacrylamide, andN-alkylacrylamides;

ethylenic monomers containing a sulphonic acid group and its ammonium oralkali metal salts, for example vinylsulphonic acid,vinylbenzenesulphonic acid, alpha-acrylamidomethylpropanesulphonic acidand 2-sulphoethylene methacrylate;

amides of vinylamine, especially vinylformamide or vinylacetamide; and

unsaturated ethylenic monomers containing a secondary, tertiary orquaternary amino group, or a heterocyclic group containing nitrogen,such as, for example, vinylpyridines, vinylimidazole, aminoalkyl(meth)acrylates and aminoalkyl (meth)acrylamides such asdimethylaminoethyl acrylate or methacrylate, di-tert-butylaminoethylacrylate or methacrylate and dimethylaminoacrylamide ordimethylaminomethacrylamide. Likewise, it is possible to usezwitterionic monomers such as, for example,sulphopropyl(dimethyl)aminopropyl acrylate.

In order to prepare the copolymers of formula (I) for which Y=H andY'=NH₂, it is preferred to use as ethylenically unsaturated monomers theamides of vinylamine, for example vinylformamide or vinylacetamide. Thecopolymer obtained is then hydrolysed to acid or basic pH.

In order to prepare the copolymers of formula (I) for which Y=H andY'=OH, it is preferred to use as ethylenically unsaturated monomersvinyl esters of carboxylic acid such as, for example, vinyl acetate. Thecopolymer obtained is then hydrolysed to acid or basic pH.

The types and amounts of copolymerizable monomers employed according tothe present invention vary depending on the particular final applicationfor which the block polymer is intended. These variations are well knownand may be easily determined by those skilled in the art.

In order for the polymer of general formula (I) to be a block polymer,the "precursor" compound of general formula (II) must be a polymer.

Thus, n is greater than or equal to 1, preferably greater than or equalto 6. The monomer units of this polymer may be identical or different.

According to the preferred embodiment of the invention, in the formula(II) for the precursor compounds, Z¹ is a sulphur atom and Z² is anoxygen atom; these compounds are therefore chain-end functionalized byalkyl xanthates.

Preferably, in the formula (II) for the precursor compounds, R¹represents:

a group of formula CR'¹ R'² R'³ in which:

R'¹, R'² and R'³ represent groups (i), (ii) or (iii) as defined above or

R'¹ =R'² =H and R'³ is an aryl, alkene or alkyne group,

or a --COR'⁴ group in which R'⁴ represents a group (i), (ii) or (iii) asdefined above.

Likewise, in the formula (II) for the precursor compounds, R² preferablyrepresents a group of formula: --CH₂ R'⁵, in which R'⁵ represents H or agroup (i), (ii) or (iii) with the exception of aryl, alkyne and alkenegroups.

The most interesting results have been obtained for compounds of formula(II) when Z¹ is a sulphur atom, Z² is an oxygen atom, R² is an ethyl orphenyl group and R¹ is a group chosen from: ##STR8##

The R¹ group may also represent a polymer chain coming from a radical orionic polymerization or coming from a polycondensation.

The compounds (II) particularly preferred are styrene (Y'=H, Y=C₆ H₅,b=0), methyl acrylate (Y'=H, Y=COOMe, b=0), ethyl acrylate (Y'=H,Y=COOEt, b=0), butyl acrylate (Y'=H, Y=COOBu, b=0), tert-butyl acrylate(Y'=H, Y=COOtBu, b=0), vinyl acetate (Y'=H, Y=OCOMe, b=0) and acrylicacid (Y'=H, Y=COOH, b=0) homopolymers, for which:

Z¹ =S, Z² =O, R¹ =CHCH₃ (CO₂ Et) and R² =Et, or

Z¹ =S, Z² =O, R¹ =CH(CO₂ Et)₂ and R² =Et.

This precursor polymer (II) may come from the radical polymerization ofan ethylenically unsaturated monomer of formula: CXX'(═CV--CV')_(b) ═CH₂by bringing the said monomer into contact with a radical polymerizationinitiator and a compound of general formula (III), (IV) or (V): ##STR9##p being between 2 and 10, preferably between 2 and 5.

In this synthesis, the radical polymerization initiators and theethylenically unsaturated monomers are of the type previously mentioned.

With regard to the compounds of general formulae (III), (IV) or (V), thesymbols R², Z², R¹ and Z¹ have the same meaning as previously. Asregards their symbols, the preferred ones are the same as previously.

Thus, the preferred compounds of general formula (III) are ethylα-(O-ethylxanthyl)propionate (Z¹ =S, Z² =O, R¹ =CHCH₃ (CO₂ Et), R² =Et)and ethyl (O-ethylxanthyl)malonate (Z¹ =S, Z² =O, R¹ =CH(CO₂ Et)₂, R²=Et).

Among compounds of formula (IV), those for which R² is the --(CH₂)_(q)-- group or a polyether group --(CHR--CH₂ --O)_(q) --CHR--CH₂ --, with qbetween 2 and 10, are preferred.

Among the compounds of formula (V), those for which R¹ is the group--CH₂ -phenyl-CH₂ -- or the group --CHCH₃ CO₂ CH₂ CH₂ CO₂ CHCH₃ -- arepreferred.

The compounds of formulae (III), (IV) and (V) are readily accessible.Those for which Z¹ is a sulphur atom and a Z² is an oxygen atom, calledalkyl xanthates, may in particular be obtained by reaction between axanthate salt, such as an alkali metal salt of the type: ##STR10## and ahalogenated derivative of the type: Hal-R¹, with Hal chosen from Cl, Bror I.

The compounds of formulae (III), (IV) and (V), in which Z¹ is S, mayalso be obtained by the process in which the following are mixed andheated:

a disulphide (S) compound of formula (A): ##STR11## and a diazo (N)compound of formula (B):

    R.sup.2 Z.sup.2 --N═N--Z.sup.2 R.sup.2

The complete process of synthesizing a block polymer of formula (I)according to the invention may therefore consist in:

(1) synthesizing a polymer by bringing into contact with each other anethylenically unsaturated monomer of formula (CXX'(═CV--CV')_(b) ═CH₂, aradical polymerization initiator and a compound of formula (III), (IV)or (V), and

(2) using the polymer obtained at step 1 as precursor of general formula(II) in order to prepare a diblock polymer by bringing it into contactwith a new ethylenically unsaturated monomer of formula:CYY'(═CW--CW')_(a) ═CH₂ and a radical polymerization initiator.

This step (2) may be repeated as many times as desired using newmonomers to synthesize new blocks and to obtain a multiblock polymer.

As indicated previously, for the preparation of precursors of formula(II) for which X=H and X'=NH₂ (step (1) defined above), it is preferredto use, as ethylenically unsaturated monomers, amides of vinylamine, forexample vinylformamide or vinylacetamide. The polymer obtained is thenhydrolysed to acid or basic pH.

Likewise, for the preparation of precursors of formula (II) for whichX=H and X'=OH, it is preferred to use vinyl esters of carboxylic acids,such as vinyl acetate for example, as ethylenically unsaturatedmonomers. The polymer obtained is then hydrolysed to acid or basic pH.

Without thereby excluding any other reaction scheme, the presumed actionmechanism of the polymerization is illustrated below in the case of axanthate-type precursor compound of formula (II).

1. Initiation of the polymerization: ##STR12##

2. Chain growth ##STR13##

3. Degenerative chain transfer ##STR14##

The degenerative chain transfer reaction makes it possible to react a"dormant" chain carrying the xanthate unit at its end into amacroradical. This unit may grow by propagation and again be added ontoa xanthate chain end, and fragment. When the xanthate exchange rate isat least as great as the propagation rate the chains will then growaccording to a controlled process. When the CH₂ ═CHR² monomer iscompletely consumed, a second monomer of a different type, CH₂ ═CHR³, isintroduced into the mixture and then block copolymers of general formula(I) are obtained: ##STR15##

According to this principle, the invention therefore also relates to aprocess for preparing multiblock polymers, in which the implementationof the process previously described is repeated at least once, using:

different monomers from those of the previous implementation, and

instead of the precursor compound of formula (II), the block polymercoming from the previous implementation.

If the implementation is repeated once, a triblock polymer will beobtained, if it is repeated twice, a "quadriblock" polymer will beobtained, and so on. In this way, at each new implementation, theproduct obtained is a block polymer having an additional polymer block.

Therefore, in order to prepare multiblock polymers, the process consistsin repeating, several times, the implementation of the preceding processon the block polymer coming from each previous implementation usingdifferent monomers.

According to this method of preparing multiblock polymers, when it isdesired to obtain homogeneous block polymers without a compositiongradient, and if all the successive polymerizations are carried out inthe same reactor, it is essential for all the monomers used in one stepto have been consumed before the polymerization of the next step starts,therefore before the new monomers are introduced.

The compounds of formula (IV) and (V) are particularly advantageous asthey allow a polymer chain to be grown on at least two active sites.With this type of compound, it is possible to save on polymerizationsteps in order to obtain an n-block copolymer.

Thus, if p=2 in the formula (IV) or (V), the first block is obtained bythe polymerization of a monomer M1 in the presence of the compound offormula (IV) or (V). This first block may then grow at each of its endsby the polymerization of a second monomer M2. A triblock copolymer isobtained, it being possible for this triblock polymer itself to grow ateach of its ends by the polymerization of a third monomer M3. Thus, a"pentablock" copolymer is obtained in only three steps.

If p is greater than 2, the process makes it possible to obtainhomopolymers or block copolymers whose structure is "multi-branched" or"hyperbranched".

The polymerization may be carried out in bulk, in solution or inemulsion. Preferably, it is carried out in emulsion.

Preferably, the process is carried out semi-continuously.

The temperature may vary between ambient temperature and 150° C.,depending on the nature of the monomers used.

In general, during the polymerization, the instantaneous polymer contentwith respect to the instantaneous amount of monomer and polymer isbetween 50 and 99% by weight, preferably between 75 and 99%, even morepreferably between 90 and 99%. Polymer is understood to mean either thecompound of formula (I) for synthesizing a block copolymer or thecompound of formula (II) for synthesizing the precursor polymer. Thiscontent is maintained, in a known manner, by controlling thetemperature, the rate of addition of the reactants and of thepolymerization initiator.

The process is carried out in the absence of a UV source.

The process according to the invention has the advantage of resulting inblock polymers having a low polydispersity index.

It also makes it possible to control the molecular mass of the polymers.

The invention therefore also relates to the block polymers which can beobtained by the above process.

In general, these polymers have a polydispersity index of at most 2,preferably of at most 1.5.

These results are especially obtained for block polymers of formula (I)which are chain-end functionalized by the alkyl xanthate group.

These polymers correspond to the polymers of general formula (I) forwhich Z¹ is a sulphur atom and Z² is an oxygen atom.

The preferred block polymers are those having at least two polymerblocks chosen from the following combinations:

polystyrene/polymethyl acrylate

polystyrene/polyethyl acrylate,

polystyrene/poly(tert-butyl acrylate),

polyethyl acrylate/polyvinyl acetate,

polybutyl acrylate/polyvinyl acetate,

polyethyl acrylate/poly(tert-butyl acrylate),

poly(tert-butyl acrylate)/polyvinyl acetate,

polyethyl acrylate/polybutyl acrylate,

polybutyl acrylate/polyvinyl alcohol,

polyacrylic acid/polyvinyl alcohol.

According to a preferred mode, the polymers have at least two polymerblocks chosen from the above combinations and are of general formula (I)in which:

Z¹ =S, Z² =O, R¹ =CHCH₃ (CO₂ Et) and R² =Et, or

Z¹ =S, Z² =O, R¹ =CH(CO₂ Et)₂ and R² =Et.

Finally, the process for synthesizing the precursor polymers of generalformula (II) also makes it possible to synthesize polymers having a lowpolydispersity index. In general, these precursor polymers have apolydispersity index of at most 2, preferably of at most 1.5, especiallywhen these polymers are alkyl-xanthate functionalized polymers (Z¹ beinga sulphur atom and Z² being an oxygen atom).

Preferably, n is greater than or equal to 6.

The compounds (II) particularly preferred are styrene (Y'=H, Y=C₆ H₅,b=0), methyl acrylate (Y'=H, Y=COOMe, b=0), ethyl acrylate (Y'=H,Y=COOEt, b=0), butyl acrylate (Y'=H, Y=COOBu, b=0), tert-butyl acrylate(Y'=H, Y=COOtBu, b=0), vinyl acetate (Y'=H, Y=OCOMe, b=0) and acrylicacid (Y'=H, Y=COOH, b=0) homopolymers, for which:

Z¹ =S, Z² =O, R¹ =CHCH₃ (CO₂ Et) and R² =Et, or

Z¹ =S, Z² =O, R¹ =CH(CO₂ Et)₂ and R² =Et.

The following examples illustrate the invention without, however,limiting the scope thereof.

EXAMPLES 1. Synthesis of (Alkyl Xanthate) Precursors of Formula (III)Example 1.1 Synthesis of the Ethyl α-(O-ethylxanthyl)propionatePrecursor

Approximately 1 liter of ethanol and 80 ml of ethyl α-bromopropionateare introduced into a round-bottomed flask. The flask is immersed in anice bath. Homogenization takes place with stirring and under a flow ofnitrogen. When the temperature of the reaction mixture has stabilized,109 g of potassium O-ethylxanthate are added. The stirring and nitrogenstream are maintained for approximately 4 hours during which the mixturebecomes whitish because of the formation of KBr.

When the reaction has reached completion, approximately 1 liter of wateris added to the reactor. The mixture becomes clear and yellow. Thedesired product is extracted from the water-alcohol phase by means of anether/pentane (1/2) mixture and recovered by vacuum evaporation.

The ¹³ C NMR spectrum gives the following peaks: 171.21; 70.11; 61.62;47.01; 16.82; 14.04; 13.60.

Example 1.2 Synthesis of the [1-(O-ethylxanthyl)ethyl]benzene Precursor

1 liter of ethanol and 80 ml of (1-bromoethyl)benzene are introducedinto a round-bottomed flask. The flask is immersed in an ice bath.Homogenization takes place with stirring and under a stream of nitrogen.When the temperature of the reaction mixture has stabilized, 104 g ofpotassium O-ethylxanthate are added. The stirring and stream of nitrogenare maintained for approximately 4 hours during which the medium becomeswhitish because of the formation of KBr.

When the reaction has reached completion, approximately 1 liter of wateris added to the reactor. The mixture becomes clear and yellow. Thedesired product is extracted from the water-alcohol phase by means of anether/pentane (1/2) mixture and recovered by vacuum evaporation.

The ¹³ C NMR spectrum gives the following peaks: 213.25; 141.73; 128.57;127.47; 126.49; 69.69; 49.21; 21.70; 13.71.

Example 1.3 Synthesis of the α,α'-di(O-ethylxanthyl)-p-xylene Precursor

Approximately 1 liter of ethanol and 80 ml of α,α'-dichloro-p-xylene areintroduced into a round-bottomed flask. The flask is immersed in an icebath. Homogenization takes place with stirring and under a stream ofnitrogen. When the temperature of the reaction medium has stabilized,184 g of potassium O-ethylxanthate are added. The stirring and stream ofnitrogen are maintained for approximately 4 hours during which themedium becomes whitish because of the formation of KCl.

When the reaction has reached completion, approximately 1 liter of wateris added to the reactor. The mixture becomes clear and yellow. Thedesired product is extracted from the water-alcohol phase by means of adichloromethane/ether/pentane (1/1/2) mixture and recovered by vacuumevaporation.

The ¹³ C NMR spectrum gives the following peaks: 135.27; 129.42; 70.23;40.12; 13.89.

Example 1.4 Synthesis of theα-(O-ethylxanthyl)-α-phthalimidoacetophenone Precursor

74 ml of acetone and 12.7 g of α-bromo-α-phthalimidoacetophenone areintroduced into a round-bottomed flask. The mixture is homogenized withstirring and under a stream of nitrogen. 6.5 g of potassiumO-ethylxanthate salt are added. The reaction lasts 5 min, after whichthe reaction mixture is diluted with distilled water.

The precipitated solid is filtered, dried and purified byrecrystallization in ethanol.

The ¹³ C NMR spectrum gives the following peaks: 210.0; 189.2; 166.2;134.4; 133.8; 133.6; 131.5; 128.7; 128.4; 123.7; 71.6; 61.8; 13.6.

Example 1.5 Synthesis of the Ethylα-(O-ethylxanthyl)-α-phenylthiopropionate Precursor

11 ml of acetone and 2.36 g of potassium O-ethylxanthate salt areintroduced into a round-bottomed flask. The mixture is homogenized withstirring and under a stream of nitrogen, and then a solution of ethylα-chloro-α-phenolthiopropionate (1.56 g) in acetone (4 ml) is added dropby drop. The mixture is stirred for 30 min. The solvent is evaporated.The residue is diluted with ether and then washed in water.

The organic phase is separated and dried on sodium sulphate. The productis recovered after concentration in vacuo and purification bychromatography on silica.

The ¹³ C NMR spectrum gives the following peaks: 211.3; 168.8; 137.6;130.4; 129.0; 128.9; 69.72; 62.99; 62.13; 25.56; 13.80; 13.37.

Example 1.6 Synthesis of the Ethyl (O-ethylxanthyl)malonate Precursor

50 ml of acetone and 4 ml of diethylchloromalonate are introduced into around-bottomed flask. The mixture is homogenized with stirring and undera stream of nitrogen and 4.4 g of potassium O-ethylxanthate salt isadded. The reaction lasts 1 hour, after which the reaction medium isdiluted with 20 ml of water.

The product is extracted from the phase thus obtained by 50 ml of ether,and then purified by flash chromatography.

The ¹³ C NMR spectrum gives the following peaks: 210.3; 165.2; 71.0;62.8; 56.4; 14.0; 13.6.

Example 1.7 Synthesis of the Ethylα-(O-phenylethylxanthyl)-α-phenylthiopropionate Precursor

20 ml of acetone and 5.58 g of potassium O-phenylethylxanthate areintroduced into a round-bottomed flask. The mixture is homogenized withstirring and under a stream of nitrogen, then the temperature is loweredto 0° C.

A solution of ethyl α-chloro-α-phenylthiopropionate (6.15 g) in acetone(20 ml) is added to the flask drop by drop. The mixture is stirred for 2hours.

Next, the solvent is evaporated. The residue is diluted with ether,washed firstly with water and then with a saturated aqueous solution ofNaCl. The organic phase is separated and dried on sodium sulphate.

The product is recovered in the form of white crystals after evaporationand recrystallization in ether at room temperature.

The ¹³ C NMR spectrum gives the following peaks: 211.27; 168.82; 130.42;69.72; 62.13; 25.56; 13.80; 13.37.

Example 1.8 Synthesis of the Ethylα-(O-phenylethylxanthyl)-α-phenylethanoate Precursor

1 equivalent of phenylethyl alcohol (16.78 ml) in solution in 150 ml ofTHF is introduced into a round-bottomed flask after which is added 1equivalent of NaH (5.68 g) at 0° C.

After 2 hours of stirring, 1 equivalent of CS₂ (8.48 ml) is added.

After stirring overnight at room temperature, the solution is filtered.The salt is washed with pentane and then dried. It is isolatedquantitatively in the form of a yellow powder, 1.09 g of which aredissolved in 5 ml of acetone. The solution is cooled to 0° C.

1 equivalent (0.99 g) of ethyl α-chlorophenylethanoate is added. Thesolution is stirred for 3 hours at room temperature.

Next, it is extracted with ether, dried on magnesium sulphate andconcentrated in vacuo.

1.62 g of ethyl α-(O-phenylethylxanthyl)-α-phenylethanoate is recovered.The overall reaction yield is 90%.

Example 1.9 Synthesis of the (O-ethylxanthyl)isobutyronitrile Precursor

10 ml of bis(O-ethyl)xanthate (2.42 g) is dissolved in 36 ml of hexanein a 100 ml round-bottomed flask provided with a refrigerant and underan inert atmosphere of argon.

The solution is heated for 15 min and then 1 equivalent ofazobis(isobutyronitrile) (AIBN) (1.64 g) is added. 0.5 equivalent ofAIBN (0.82 g) is added after two and a half hours.

The solution is dried under vacuum. The product is purified bychromatography and isolated. The yield is 77%.

Example 1.10 Synthesis of the Ethyl (O-neopentylxanthyl)malonatePrecursor

1 equivalent of neopentyl alcohol (2.15 ml) in solution in 30 ml of THFis introduced into a round-bottomed flask. 1 equivalent of NaH (0.81 g)is then added at 0° C.

After two hours of stirring, 1 equivalent of CS₂ (1.21 ml) is added.

After stirring overnight at room temperature, the solution is filtered.The salt is washed with pentane and then dried. It is isolatedquantitatively in the form of a yellow powder, 1.86 g of which isdissolved in 10 ml of acetone. The solution is cooled to 0° C.

1 equivalent of ethylchloromalonate (1.61 ml) in 5 ml of acetone isadded. The solution is stirred for 4 hours at room temperature. It isthen hydrolysed and extracted with ether. It is then dried on magnesiumsulphate and concentrated in vacuo.

After purification by chromatography, 2.08 g of product is isolated. Theyield is 65%.

Example 1.11 Synthesis of the Ethyl (O-isobornylxanthyl)malonatePrecursor

15.4 g of isoborneol in solution in 200 ml of THF are introduced into around-bottomed flask. The solution is treated with 1 equivalent of NaHat 0° C. then, after 2 hours of stirring, 6 ml of CS₂ are added.

The solution is stirred overnight at room temperature and then filtered.The salts are then washed with ether. The filtrate is concentrated. Itis taken up in pentane and filtered. Finally, it is dried in order toobtain the sodium salt quantitatively.

5.04 g of this salt are dissolved in 40 ml of acetone. The solution iscooled to 0° C. 3.08 ml of ethylchloromalonate are added. The solutionis stirred for one hour at 0° C. Next, it is hydrolysed, extracted withether and then dried on magnesium sulphate and concentrated in vacuo.

After purification by chromatography on silica, 5.92 g of product areobtained. The yield is 80%.

Example 1.12 Synthesis of the (O-isopropylxanthyl)valeronitrilePrecursor

0.336 g of azobisvaleronitrile and 0.27 g of bis(O-isopropyl)xanthateare dissolved in dioxane. The temperature is raised to 101° C.

After 12 hours of stirring, the solvent is evaporated and the residuepurified by chromatography on silica.

The product is obtained with a 60% yield.

Example 2 Synthesis of the Precursors of Formula (II) (Homopolymers)Example 2.1 Styrene Homopolymer

1 mmol of ethyl α-(O-ethylxanthyl)propionate (0.222 g) and 40 mmol ofstyrene (4.16 g) are introduced into a 10 ml round-bottomed flask. Thetemperature is raised to 125° C. and 0.03 mmol of lauroyl peroxide (12.8mg) are added.

The polymerization lasts 9 hours, after which several additions ofinitiator are made:

0.02 mmol after two hours,

0.02 mmol after four hours,

0.01 mmol after six hours,

0.01 mmol after eight hours.

The polymer is recovered by precipitation in methanol and analysed byGPC in a THF medium and in polystyrene equivalents (see Table 9).

Example 2.2 Styrene Homopolymer

1 mmol of [1-(O-ethylxanthyl)ethyl]benzene (0.226 g) and 40 mmol ofstyrene (4.16 g) are introduced into a 10 ml round-bottomed flask. Thetemperature is raised to 90° C. and 0.02 mmol of lauroyl peroxide (8.52mg) are added.

The polymerization lasts 12 hours, during which several additions ofinitiator are made:

0.01 mmol after two hours,

0.01 mmol after four hours,

0.01 mmol after six hours,

0.01 mmol after eight hours,

0.01 mmol after ten hours.

The polymer is recovered by precipitation in methanol and analysed byGPC in a THF medium and in polystyrene equivalents (see Table 9).

Example 2.3 Styrene Homopolymer

1 mmol of α,α'-di(O-ethylxanthyl)-p-xylene (0.346 g) and 40 mmol ofstyrene (4.16 g) are introduced into a 10 ml round-bottomed flask. Thetemperature is raised to 90° C. and 0.02 mmol of lauroyl peroxide (8.52mg) are added.

The polymerization lasts 15 hours, during which several additions ofinitiator are made:

0.01 mmol after two hours,

0.01 mmol after four hours,

0.01 mmol after six hours,

0.01 mmol after eight hours,

0.01 mmol after twelve hours,

0.01 mmol after fourteen hours.

The polymer is recovered by precipitation in methanol and analysed byGPC in a THF medium and in polystyrene equivalents (see Table 9).

Example 2.4 Styrene Homopolymer

1 mmol of α-(O-ethylxanthyl)-α-phthalimidoacetophenone (0.385 g) and 40mmol of styrene (4.16 g) are introduced into a 10 ml round-bottomedflask. The temperature is raised to 90° C. and 0.02 mmol of lauroylperoxide (8.52 mg) are added.

The polymerization lasts 15 hours, during which several additions ofinitiator are made:

0.01 mmol after two hours,

0.01 mmol after four hours,

0.01 mmol after six hours,

0.01 mmol after eight hours,

0.01 mmol after twelve hours,

0.01 mmol after fourteen hours.

The polymer is recovered by precipitation in methanol and analysed byGPC in a THF medium and in polystyrene equivalents (see Table 9).

Example 2.5 Styrene Homopolymer

1 mmol of ethyl α-(O-ethylxanthyl)-α-phenylthiopropionate (0.33 g) and40 mmol of styrene (4.16 g) are introduced into a 10 ml round-bottomedflask. The temperature is raised to 90° C. and 0.02 mmol of lauroylperoxide (8.52 mg) are added.

The polymerization lasts 15 hours, during which several additions ofinitiator are made:

0.01 mmol after two hours,

0.01 mmol after four hours,

0.01 mmol after six hours,

0.01 mmol after eight hours,

0.01 mmol after twelve hours,

0.01 mmol after fourteen hours.

The polymer is recovered by precipitation in methanol and analysed byGPC in a THF medium and in polystyrene equivalents (see Table 9).

Example 2.6 Methyl Acrylate Homopolymer

1 mmol of ethyl α-(O-ethylxanthyl)propionate (0.222 g), 40 mmol ofmethyl acrylate (MeA) (3.44 g) and 3.5 ml of toluene are introduced intoa 10 ml round-bottomed flask. The temperature is raised to 100° C. and0.035 mmol of lauroyl peroxide (14.9 mg) are added. The polymerizationlasts 15 hours, during which several additions of initiator are made:

0.02 mmol after two hours,

0.02 mmol after six hours,

0.02 mmol after ten hours.

The polymer is recovered by evaporating, under high vacuum, the solventand the traces of residual monomers and is analysed by GPC in THF mediumand polystyrene equivalents (see Table 9).

Example 2.7 Methyl Acrylate Homopolymer

1 mmol of ethyl α-(O-ethylxanthyl)propionate (0.222 g) and 40 mmol ofmethyl acrylate (3.44 g) are introduced into a 10 ml round-bottomedflask. The temperature is raised to 80° C. and 0.03 mmol of lauroylperoxide (12.8 mg) are added.

The polymerization lasts 45 min.

The polymer is recovered by evaporating, under high vacuum, the solventand the traces of residual monomers. It is analysed by GPC in THF mediumand in polystyrene equivalents (see Table 9).

Example 2.8 Methyl Acrylate Homopolymer

1 mmol of ethyl α-(O-ethylxanthyl)propionate (0.222 g) and 80 mmol ofmethyl acrylate (6.88 g) are introduced into a 10 ml round-bottomedflask. The temperature is raised to 80° C. and 0.02 mmol of lauroylperoxide (8.52 mg) are added. The polymerization lasts 45 min.

The polymer is recovered by evaporating, under high vacuum, the tracesof residual monomers. It is analysed by GPC in THF medium and inpolystyrene equivalents (see Table 9).

Example 2.9 Methyl Acrylate Homopolymer

1 mmol of α-(O-ethylxanthyl)-α-phthalimidoacetophenone (0.385 g) and 40mmol of methyl acrylate (3.44 g) are introduced into a 10 mlround-bottomed flask. The temperature is raised to 80° C. and 0.02 mmolof lauroyl peroxide (8.52 mg) are added. The polymerization lasts 45min.

The polymer is recovered by evaporating, under high vacuum, the tracesof residual monomers. It is analysed by GPC (see Table 9).

Example 2.10 Ethyl Acrylate Homopolymer

1 mmol of ethyl α-(O-ethylxanthyl)propionate (0.222 g) and 40 mmol ofethyl acrylate (EtA) (3.44 g) are introduced into a 10 ml round-bottomedflask. The temperature is raised to 80° C. and 0.02 mmol of lauroylperoxide (8.52 mg) are added. The polymerization lasts 6 hours.

The polymer is recovered by evaporating, under high vacuum, the tracesof residual monomers. It is analysed by GPC in THF medium and inpolystyrene equivalents (see Table 9).

Example 2.11 Methyl Acrylate Homopolymer

1 mmol of ethyl α-(O-ethylxanthyl)-α-phenylthiopropionate (0.33 g) and40 mmol of methyl acrylate (3.44 g) are introduced into a 10 mlround-bottomed flask. The temperature is raised to 80° C. and 0.02 mmolof lauroyl peroxide (8.52 mg) are added.

The polymerization lasts 6 hours.

The polymer is recovered by evaporating, under high vacuum, the tracesof residual monomers. It is analysed by GPC in THF medium and inpolystyrene equivalents (see Table 9).

Example 2.12 2-Ethylhexyl Acrylate Homopolymer

1 mmol of ethyl (O-ethylxanthyl)malonate (0.28 g) and 40 mmol of2-ethylhexyl acrylate (2EHA) (7.36 g) are introduced into a 10 mlround-bottomed flask. The temperature is raised to 80° C. and 0.02 mmolof lauroyl peroxide (8.52 mg) are added.

The polymerization lasts 6 hours.

The polymer is recovered by evaporating, under high vacuum, the tracesof residual monomers. It is analysed by GPC in THF medium and inpolystyrene equivalents (see Table 9).

Example 2.13 Vinyl Acetate Homopolymer

1 mmol of ethyl α-(O-ethylxanthyl)propionate (0.222 g) and 40 mmol ofvinyl acetate (VA) (3.44 g) are introduced into a 10 ml round-bottomedflask. The temperature is raised to 80° C. and 0.02 mmol of lauroylperoxide (8.52 mg) are added.

The polymerization lasts 8 hours, during which several additions ofinitiator are made:

0.01 mmol after two hours,

0.01 mmol after four hours,

0.01 mmol after six hours.

The polymer is recovered by evaporating, under high vacuum, the tracesof residual monomers and analysed by GPC in THF medium and inpolystyrene equivalents (see Table 9).

Example 2.14 Vinyl Acetate Homopolymer

1 mmol of ethyl α-(O-ethylxanthyl)propionate (0.222 g) and 40 mmol ofvinyl acetate (3.44 g) are introduced into a 10 ml round-bottomed flask.The temperature is raised to 80° C. and 0.02 mmol of lauroyl peroxide(8.52 mg) are added.

The polymerization lasts 4 hours.

The polymer is recovered by evaporating, under high vacuum, the tracesof residual monomers. It is analysed by GPC in THF medium and inpolystyrene equivalents (see Table 9).

Example 2.15 Styrene Homopolymer

1 mmol (3.8 g) of the polymer from Example 2.1, chain-end functionalizedby the O-ethylxanthyl group, and 40 mmol of styrene (4.16 g) areintroduced into a 10 ml round-bottomed flask. The temperature is raisedto 90° C. and 0.02 mmol of lauroyl peroxide (8.52 mg) are added.

The polymerization lasts 10 hours, during which several additions ofinitiator are made:

0.01 mmol after two hours,

0.01 mmol after four hours,

0.01 mmol after six hours,

0.01 mmol after eight hours.

The polymer is recovered by precipitation in methanol and analysed byGPC in THF medium and in polystyrene equivalents (see Table 9).

This polymer is a styrene homopolymer, but it was obtained as a diblockcopolymer with two polystyrene blocks.

Example 2.16 Styrene Homopolymer

The following are introduced into a 2 l reactor:

0.4 g of sodium bicarbonate,

5.4 g of sodium lauryl sulphate, and

1020 g of water.

The temperature is increased to 85° C.

An aqueous ammonium persulphate solution (1.6 g of water+0.8 g ofammonium persulphate) is added.

A mixture containing 400 g of styrene and 2.22 g of ethylα-(O-ethylxanthyl)propionate is added continuously over a period of 2hours.

The temperature is maintained at 85° C. for an additional 1 hour, duringwhich an aqueous ammonium persulphate solution (0.8 g of water+0.4 g ofammonium persulphate) is introduced.

The polymer obtained is recovered after coagulation of the emulsion andanalysed by GPC in THF medium and in polystyrene equivalents (see Table9).

Example 2.17 Styrene Homopolymer

1 mmol of ethyl (O-ethylxanthyl)malonate (0.28 g) and 40 mmol of styrene(4.16 g) are introduced into a 10 ml round-bottomed flask. Thetemperature is raised to 95° C. and 0.03 mmol of lauroyl peroxide (12.8mg) are added.

The polymerization lasts 10 hours, during which several additions ofinitiator are made:

0.02 mmol after two hours,

0.02 mmol after four hours,

0.02 mmol after six hours,

0.02 mmol after eight hours.

The polymer is recovered by precipitation in methanol.

It is analysed by GPC in THF medium and in polystyrene equivalents (seeTable 9).

Example 2.18 Methyl Acrylate Homopolymer

1 mmol of ethyl (O-ethylxanthyl)malonate (0.28 g) and 40 mmol of methylacrylate (3.44 g) are introduced into a 10 ml round-bottomed flaskcontaining 4 ml of toluene. The temperature is raised to 80° C. and 0.03mmol of lauroyl peroxide (12.8 mg) are added.

The polymerization lasts 26 hours, during which 0.02 mmol of lauroylperoxide are added every two hours.

The polymer is recovered by evaporating, under high vacuum, the tolueneand the traces of residual monomer.

It is analysed by GPC in THF medium and in polystyrene equivalents (seeTable 9).

Example 2.19 Styrene Homopolymer

1 mmol of ethyl α-(O-phenylethyl)-α-phenylthiopropionate (0.406 g) and40 mmol of styrene (4.16 g) are introduced into a 10 ml round-bottomedflask. The temperature is raised to 95° C. and 0.03 mmol of lauroylperoxide (12.8 mg) are added.

The polymerization lasts 16 hours, during which 0.02 mmol of lauroylperoxide are added every two hours.

The polymer is recovered by precipitation in methanol.

It is analysed by GPC in THF medium and in polystyrene equivalents (seeTable 9).

Example 2.20 Methyl Acrylate Homopolymer

1 mmol of ethyl α-(O-phenylethylxanthyl)-α-phenylethanoate (0.36 g) and40 mmol of methyl acrylate (3.44 g) are introduced into a 10 mlround-bottomed flask. The temperature is raised to 80° C. and 0.03 mmolof lauroyl peroxide (12.8 mg) are added.

The polymerization lasts 11 hours, during which 0.02 mmol of lauroylperoxide are added every two hours.

The polymer is recovered by evaporating, under high vacuum, the tracesof residual monomer.

It is analysed by GPC in THF medium and in polystyrene equivalents (seeTable 9).

Example 2.21 Methyl Acrylate Homopolymer

1 mmol of (O-ethylxanthyl)isobutyronitrile (0.189 g) and 40 mmol ofmethyl acrylate (3.44 g) are introduced into a 10 ml round-bottomedflask. The temperature is raised to 80° C. and 0.03 mmol of lauroylperoxide (12.8 mg) are added.

The polymerization lasts 6 hours, during which 0.02 mmol of lauroylperoxide are added every two hours, after 2 and 4 hours.

The polymer is recovered by evaporating, under high vacuum, the tracesof residual monomers.

It is analysed by GPC in THF medium and in polystyrene equivalents (seeTable 9).

Example 2.22 Methyl Acrylate Homopolymer

1 mmol of ethyl (O-neopentylxanthyl)malonate (0.322 g) and 40 mmol ofmethyl acrylate (3.44 g) are introduced into a 10 ml round-bottomedflask. The temperature is raised to 80° C. and 0.03 mmol of lauroylperoxide (12.8 mg) are added.

The polymerization lasts 4 hours, during which 0.02 mmol of lauroylperoxide are added after two hours.

The polymer is recovered by evaporating, under high vacuum, the tracesof residual monomer.

It is analysed by GPC in THF medium and in polystyrene equivalents (seeTable 9).

Example 2.23 Methyl Acrylate Homopolymer

1 mmol of ethyl (O-isobornylxanthyl)malonate (0.388 g) and 40 mmol ofmethyl acrylate (3.44 g) are added to a 10 ml round-bottomed flask. Thetemperature is raised to 80° C. and 0.03 mmol of lauroyl peroxide (12.8mg) are added.

The polymerization lasts 2 hours 30 minutes during which 0.02 mmol oflauroyl peroxide are added after 2 hours.

The polymer is recovered by evaporating, under high vacuum, the tracesof residual monomer.

It is analysed by GPC in THF medium and in polystyrene equivalents (seeTable 9).

Example 2.24 Vinyl Acetate Homopolymer

1 mmol of ethyl (O-isobornyl)malonate (0.388 g) and 77 mmol of vinylacetate (6.62 g) are introduced into a 10 ml round-bottomed flask. Thetemperature is raised to 70° C. and 0.01 mmol of AIBN(azobisisobutyronitrile) (1.64 mg) are added. The polymerization lasts24 hours, during which several additions of AIBN are made:

1.4 mg after two hours,

2.2 mg after four hours.

The polymer is recovered by evaporating, under high vacuum, the tracesof residual monomers.

It is analysed by GPC in THF medium and in polystyrene equivalents (seeTable 9).

Example 2.25 Acrylic Acid Homopolymers

25 g of acrylic acid are dissolved in 85 g of water and then thesolution thus obtained is neutralized to a pH between 6 and 7: thissolution is solution 1.

0.35 g of 2,2'-azobis(2-methylpropionamide)dihydrochloride are dissolvedin 150 g of water: this solution is solution 2.

Into three round-bottomed flasks, each containing a different quantityof (O-isopropylxanthyl)valeronitrile, are introduced 11 g of solution 1and 1.5 g of solution 2. The compositions of the various flasks areshown in Table A.

The temperature is raised to 70° C. and polymerization is carried outover 24 hours.

The polymer is recovered by evaporating, under high vacuum, the waterand the traces of residual monomer.

It is analysed by GPC in aqueous medium and in PEO equivalents, theresults being given in Table 1.

                  TABLE 1                                                         ______________________________________                                        Mass of precursor                                                                         Degree of conversion                                              (g)         (%)             M.sub.n PI                                        ______________________________________                                        0.065       100             14,800  1.7                                       0.108       100             12,000  1.4                                       0.163       100              8,900  1.4                                       ______________________________________                                    

Example 2.26 Acrylic Acid Homopolymer

1 mmol of ethyl α-(O-ethylxanthyl)propionate (0.222 g) and 40 mmol ofacrylic acid (2.88 g) are introduced into a 10 ml round-bottomed flask.The temperature is raised to 80° C. and 0.04 mmol of lauroyl peroxide(17 mg) are added.

The polymerization lasts 6 hours, during which several additions oflauroyl peroxide are made:

0.04 mmol after two hours,

0.04 mmol after four hours.

The polymer is recovered by evaporating, under high vacuum, the tracesof residual monomer.

It is analysed by GPC in aqueous medium and in PEO equivalents (seeTable 9).

Example 2.27 Acrylic Acid Homopolymers

Several acrylic acid homopolymers are prepared in the following manner.

All the acrylic acid (AA), the AIBN and the ethylα-(O-ethylxanthyl)propionate precursor are mixed together and introducedinto a round-bottomed flask. The amounts are given in Table 2. Thetemperature is raised to 80° C.

The polymerization lasts 6 hours.

The traces of residual monomer are removed by evaporation.

The results, obtained from GPC analysis in THF medium and in polystyreneequivalents, are given in Table 2.

                  TABLE 2                                                         ______________________________________                                        AA mass  AIBN mass Precursor mass                                             (g)      (mg)      (g)          M.sub.n                                                                             PI                                      ______________________________________                                        1.53     3.47      0.35         345   1.12                                    3.39     1.81      0.2          770   1.10                                    3.85     1.15      0.13         1060  1.25                                    4.08     0.92      0.10         1290  1.30                                    ______________________________________                                    

Example 2.28 Acrylic Acid Homopolymers

Several acrylic acid homopolymers are prepared in solution in thefollowing manner.

All the acrylic acid (AA), the AIBN and the ethylα-(O-ethylxanthyl)propionate precursor are dissolved in acetone in around-bottomed flask. The respective amounts of each ingredient aregiven in Table 3.

The temperature is raised to 60° C.

The polymerization lasts 3 hours.

The traces of residual monomer and the solvent are removed byevaporation.

The results, obtained by GPC analysis in THF medium and in polystyreneequivalents, are given in Table 3.

                  TABLE 3                                                         ______________________________________                                                          Precursor                                                                              Volume of                                          AA mass                                                                              AIBN mass  mass     solvent                                            (g)    (mg)       (g)      (ml)    M.sub.n                                                                             PI                                   ______________________________________                                        5.07   2.93       0.3      8        550  1.10                                 3.88   1.12       0.12     5       1170  1.19                                 4.37   0.63       0.07     5       1760  1.29                                 4.56   0.44       0.05     5       1920  1.27                                 ______________________________________                                    

Example 2.29 Ethyl Acrylate Homopolymer

The following are introduced into a round-bottomed flask:

33.2 mg of ethyl α-(O-ethylxanthyl)propionate (1 equivalent),

5.01 g of ethyl acrylate (160 equivalents), and

8.2 mg of AIBN.

The temperature is raised to 70° C. The polymerization lasts 24 hours.

The polymer is recovered by evaporating, under high vacuum, the tracesof residual monomer. It is analysed by GPC in THF medium and inpolystyrene equivalents (see Table 9).

Example 2.30 Vinyl Acetate Homopolymer

4.3 g of vinyl acetate and 59.7 mg of lauroyl peroxide are introducedinto three round-bottomed flasks containing varying amounts of ethylα-(O-ethylxanthyl)propionate. The temperature is raised to 70° C. andthe polymerization lasts 6 hours. The amounts of precursor used aregiven in Table 4.

The polymer is recovered by evaporating, under high vacuum, the tracesof residual monomer. The results, obtained by GPC analysis in THF mediumand in polystyrene equivalents, are given in Table 4.

                  TABLE 4                                                         ______________________________________                                        Mass of precursor                                                                         Degree of conversion                                              (g)         (%)             M.sub.n PI                                        ______________________________________                                        0.266       64.4            2100    1.4                                       0.130       66.6            4100    1.6                                       0.068       66.0            7000    1.9                                       ______________________________________                                    

Example 2.31 Styrene Homopolymer Obtained in Emulsion

The following are introduced into a 1.5 l reactor fitted with a Teflon(PTFE) anchor stirrer:

525 g of water,

0.2 g of sodium hydrogen carbonate and

10 g of sodium lauryl sulphate.

The temperature is raised to 70° C. and 20 g of styrene and all of theethyl α-(O-ethylxanthyl)propionate precursor are added in one go.

Next, the temperature is increased to 85° C. and 0.4 g of ammoniumpersulphate in solution in 16.13 g of water are added in one go.

Styrene (180 g) is then continuously fed in over a period of four hours.

The temperature is maintained at 85° C. for an additional 2 hours.

The results, obtained from GPC analysis in THF medium and in polystyreneequivalents, are given in Table 5.

                  TABLE 5                                                         ______________________________________                                        Mass of precursor                                                                         Degree of conversion                                              (g)         (%)             M.sub.n PI                                        ______________________________________                                        2           88              15,400  1.9                                       1           90              29,500  1.9                                       ______________________________________                                    

Example 2.32 Styrene Homopolymer Obtained in Emulsion

The following are introduced into a 1.5 l reactor fitted with a Teflon(PTFE) anchor stirrer:

475 g of water,

0.2 g of sodium hydrogencarbonate and

10 g of sodium lauryl sulphate.

The temperature is raised to 70° C. and the following are added in onego:

20 g of styrene and

2 g of ethyl α-(O-ethylxanthyl)propionate.

Next, the temperature is increased to 85° C. and 0.4 g of ammoniumpersulphate in solution in 16.13 g of water are added in one go.

The following are introduced into the reactor, continuously andsimultaneously:

180 g of styrene over 8 hours,

0.4 g of ammonium persulphate in 50.4 g of water over 10 hours.

Specimens are removed regularly and analysed by GPC in THF medium and inpolystyrene equivalents. The results obtained are given in Table 6.

                  TABLE 6                                                         ______________________________________                                        Time (h) Degree of conversion (%)                                                                        M.sub.n  PI                                        ______________________________________                                        1        10.1              2500     1.8                                       2        18.6              3300     1.8                                       4        39.2              6250     1.9                                       6        56.3              8100     1.9                                       8        73.3              10,000   1.9                                       24       75.7              10,500   1.9                                       ______________________________________                                    

A linear increase in the molecular masses with conversion is observed,thereby demonstrating the controlled character of the radicalpolymerization.

Example 2.33 Ethyl Acrylate Homopolymer

A solution is prepared which contains:

17.64 g of ethyl acrylate;

0.459 g of ethyl α-(O-ethylxanthyl)propionate and

0.036 g of AIBN.

1 g of this solution is introduced into 7 tubes which will serve todetermine the polymerization kinetics.

These tubes are then heated to 70° C. and stopped at different times.For each tube, the polymer is recovered by evaporating the traces ofresidual monomer and analysed by GPC in THF medium and in polystyreneequivalents.

The results obtained are given in Table 7.

                  TABLE 7                                                         ______________________________________                                        Time (min)                                                                             Degree of conversion (%)                                                                        M.sub.n  PI                                        ______________________________________                                        12       0                 1900     3.4                                       21       17                4200     2.5                                       30       32.3              4300     2.5                                       42       43.5              4800     2.4                                       53       46.6              4800     2.5                                       66       71.4              6700     1.9                                       124      80.4              7100     1.9                                       ______________________________________                                    

A linear increase in the molecular masses with conversion is observed,thereby demonstrating the controlled character of the radicalpolymerization.

Example 2.34 Vinyl Acetate Homopolymer

A solution is prepared which contains:

7.35 g of vinyl acetate,

0.229 g of ethyl α-(O-ethylxanthyl)propionate, and

0.018 g of AIBN.

1 g of this solution is introduced into 4 tubes which will serve todetermine the polymerization kinetics.

The tubes are then heated to 70° C. and stopped at different times. Foreach tube, the polymer is recovered by evaporating the traces ofresidual monomer and analysed by GPC in THF medium and in polystyreneequivalents.

The results obtained are given in Table 8.

                  TABLE 8                                                         ______________________________________                                        Time (min)                                                                             Degree of conversion (%)                                                                        M.sub.n  PI                                        ______________________________________                                        12       0                                                                    28       13.8              1200     1.4                                       38       77.8              4300     1.7                                       51       83.9              4300     1.7                                       ______________________________________                                    

A linear increase in the molecular masses with conversion is observed,thereby demonstrating the controlled character of the radicalpolymerization.

Results of Examples 2.1 to 2.24, 2.26 and 2.29

GPC analysis of the homopolymers obtained above is used to measure theirnumber-average mass (M_(n)). It is also used to measure theirweight-average mass (M_(w)) and hence their polydispersity index (PI)corresponding to the ratio of M_(w) to M_(n).

GPC chromatograms are systematically produced in double detection mode,namely refractometry (RI) and UV absorption (UV). The UV detectionwavelength corresponds to the maximum absorption of the xanthatefunctional group fixed on the end of the chain according to the formulaclaimed. For all the specimens analysed, there is perfect superpositionof the chromatograms obtained from one or other detection mode. Thisresult indicates that the chain ends are functionalized and constitutesan additional proof of the assumed structure of the polymers accordingto the invention.

                  TABLE 9                                                         ______________________________________                                                                           Degree of                                  Examples   Monomer  M.sub.n   PI   conversion                                 ______________________________________                                        Ex. 2.1    styrene  3800      2                                               Ex. 2.2    styrene  5200      2.1                                             Ex. 2.3    styrene  7900      2.5                                             Ex. 2.4    styrene  3200      1.8                                             Ex. 2.5    styrene  3300      1.9                                             Ex. 2.6    MeA      3500      1.8                                             Ex. 2.7    MeA      3750      1.7                                             Ex. 2.8    MeA      7300      1.7                                             Ex. 2.9    MeA      3000      1.4                                             Ex. 2.10   EtA      3700      1.6                                             Ex. 2.11   MeA      3500      1.35                                            Ex. 2.12   2EHA     6900      1.5                                             Ex. 2.13   VA       3200      1.35                                            Ex. 2.14   VA       2100      1.18                                            Ex. 2.15   styrene  6200      2                                               Ex. 2.16   styrene  3800      1.6                                             Ex. 2.17   styrene  4300      1.9  78                                         Ex. 2.18   MeA      3900      1.5  95                                         Ex. 2.19   styrene  3400      1.8  77                                         Ex. 2.20   MeA      3100      1.6  60                                         Ex. 2.21   MeA      3600      1.4  75                                         Ex. 2.22   MeA      5100      1.4  90                                         Ex. 2.23   MeA      4000      1.7  88                                         Ex. 2.24   VA ?     2500      1.8  29                                         Ex. 2.26   AA       6600      2.3  97                                         Ex. 2.29   EtA      29,400    1.9  93                                         ______________________________________                                    

Example 2.35 Vinyl Acetate Homopolymer

The following are introduced into a 10 ml round-bottomed flask:

0.899 g of vinyl acetate (i.e. approximately 10 equivalents),

0.220 g of ethyl α-(O-ethylxanthylpropionate (1 equivalent), and

17.2 mg of AIBN.

The temperature is raised to 70° C. The polymerization lasts 24 hours.

The polymer is recovered by evaporating, under high vacuum, the tracesof residual monomer and is analysed by MALDI-TOF on a DHB(dihydroxybenzoic acid) matrix. The results are given in Table 10.

                  TABLE 10                                                        ______________________________________                                        Number of VA                                                                              Theoretical mass                                                                          MALDI-TOF mass                                        units       (g)         (g)                                                   ______________________________________                                        7           833         831.556                                               8           919         917.458                                               9           1005        1003.638                                              ______________________________________                                    

In Table 10, the theoretical masses are calculated assuming a structureaccording to the formula: ##STR16##

It is necessary to add 23 g to the mass obtained since the speciesdetected are in sodium salt form. The excellent agreement between thetheoretical masses and the masses measured by MALDI-TOF confirm theassumed mechanism for the polymerization and the structure of thepolymers obtained.

Examples 3 Synthesis of Block Copolymers Example 3.1 p(MeA-b-St) BlockCopolymer

The following are introduced into a 10 ml round-bottomed flask:

1 mmol of ethyl α-(O-ethylxanthyl)propionate (0.222 g) and

20 mmol of methyl acrylate (1.72 g).

The mixture is heated to 80° C. and 0.02 mmol of lauroyl peroxide (8.52mg) are added. The mixture is maintained at temperature for 45 min afterwhich it coagulates. Next, the reaction mixture is dissolved in 3 ml oftoluene and then evaporated to dryness, in vacuo. This operation isrepeated three times in order to remove the traces of residual methylacrylate. This synthesis results in a precursor which can be used forpreparing a block copolymer.

Next, 20 mmol of styrene (2.08 g) are introduced into the reactor. Thetemperature is raised to 110° C. and 0.02 mmol of lauroyl peroxide (8.52mg) are added. This second step lasts 6 hours, during which severaladditions of initiator are made:

0.01 mmol after two hours,

0.01 mmol after four hours.

The copolymer obtained is recovered by precipitation in methanol andanalysed by double detection GPC--refractometry and UV spectrometry. TheGPC solvent is THF and the masses are given in polystyrene equivalents.The results are given in Table 12.

Example 3.2 p(St-b-MeA) Block Copolymer

The following are introduced into a 10 ml round-bottomed flask:

1 mmol of ethyl α-(O-ethylxanthyl)propionate (0.222 g),

20 mmol of styrene (2.08 g), and

1 ml of toluene.

The reaction mixture is raised to 110° C. and 0.025 mmol of lauroylperoxide (10.6 mg) are introduced into the reactor. This first steplasts 9 hours, during which several additions of initiator are made:

0.01 mmol after two hours,

0.01 mmol after four hours,

0.01 mmol after six hours,

0.01 mmol after eight hours.

Next, the mixture is cooled to 80° C. and the following are introduced:

20 mmol of methyl acrylate (1.72 g) and

0.03 mmol of lauroyl peroxide (12.8 mg).

This second step lasts 7 hours, during which several additions ofinitiator are made:

0.01 mmol after two hours,

0.01 mmol after four hours,

0.01 mmol after six hours.

The polymer obtained is recovered and analysed as in Example 3.1. Theresults are given in Table 11.

Example 3.3 p(St-b-MeA) Block Copolymer

The following are introduced into a 10 ml round-bottomed flask:

1 mmol of [1-(O-ethylxanthyl)ethyl]benzene (0.226 g) and

20 mmol of styrene (2.08 g).

The temperature is raised to 90° C. and 0.03 mmol of lauroyl peroxide(12.8 mg) are added. The temperature is maintained at 90° C. for 10hours, during which several additions of initiator are made:

0.01 mmol after two hours,

0.01 mmol after four hours,

0.01 mmol after six hours,

0.01 mmol after eight hours.

Next, the reaction mixture is cooled to 80° C. and the following areintroduced:

20 mmol of methyl acrylate (1.72 g) and

0.02 mmol of lauroyl peroxide (8.52 mg).

This second step lasts 8 hours, during which several additions ofinitiator are made:

0.01 mmol after two hours,

0.01 mmol after four hours,

0.01 mmol after six hours,

0.01 mmol after seven hours.

The polymer obtained is recovered and analysed as in Example 3.1. Theresults are given in Table 12.

Example 3.4 p(St-b-MeA-b-St) Block Copolymer

The following are introduced into a 10 ml round-bottomed flask:

1 mmol of [1-(O-ethylxanthyl)ethyl]benzene (0.226 g) and

20 mmol of styrene (2.08 g).

The temperature is raised to 90° C. and 0.03 mmol of lauroyl peroxide(12.8 mg) are added. The temperature is maintained at 90° C. for 10hours, during which several additions of initiator are made:

0.01 mmol after two hours,

0.01 mmol after four hours,

0.01 mmol after six hours,

0.01 mmol after eight hours.

Next, the reaction mixture is cooled to 80° C. and the following areintroduced:

20 mmol of methyl acrylate and

0.02 mmol of lauroyl peroxide.

This second step lasts 8 hours, during which several additions ofinitiator are made:

0.01 mmol after two hours,

0.01 mmol after four hours,

0.01 mmol after six hours,

0.01 mmol after seven hours.

The temperature is again raised to 90° C. and the following areintroduced:

20 mmol of styrene (2.08 g) and

0.02 mmol of lauroyl peroxide.

This third step lasts 8 hours, during which several additions ofinitiator are made:

1 mmol after two hours,

1 mmol after four hours,

1 mmol after six hours.

The polymer obtained is recovered and analysed as in Example 3.1. Theresults are given in Table 12.

Example 3.5 p(MeA-b-St) Block Copolymer

The following are introduced into a round-bottomed flask:

1 mmol of [1-(O-ethylxanthyl)ethyl]benzene (0.226 g) and

20 mmol of methyl acrylate (1.72 g).

The temperature is raised to 80° C. and 0.02 mmol of lauroyl peroxideare added. This first step lasts 8 hours, during which several additionsof initiator are made:

1 mmol after two hours,

1 mmol after four hours,

1 mmol after six hours.

Next, the temperature is increased to 90° C. and the following areintroduced:

20 mmol of styrene and

0.02 mmol of lauroyl peroxide; This second step lasts 14 hours, duringwhich several additions of initiator are made:

0.01 mmol after two hours,

0.01 mmol after four hours,

0.01 mmol after six hours,

0.01 mmol after eight hours,

0.01 mmol after ten hours,

0.01 mmol after twelve hours.

The polymer obtained is recovered and analysed as in Example 3.1. Theresults are given in Table 12.

Example 3.6 p(EtA-b-VA) Block Copolymer

The following are introduced into a round-bottomed flask:

1.881 g of ethyl acrylate,

0.111 g of ethyl α-(O-ethylxanthyl)propionate and

8.6 mg of lauroyl peroxide.

The temperature is raised to 80° C. The polymerization lasts 6 hours,during which several additions of lauroyl peroxide are made:

9.2 mg after 2 hours,

9.0 mg after 4 hours.

After cooling, the traces of residual ethyl acrylate are removed byevaporation under high vacuum and a small fraction of the polymer istaken for GPC analysis in THF medium and in polystyrene equivalents. Theresults are as follows:

degree of conversion: 98.3%

M_(n) =2800

PI=1.8.

Next, 1.853 g of vinyl acetate and 8.6 mg of lauroyl peroxide areintroduced into the flask. The temperature is raised to 80° C. Thepolymerization lasts 6 hours, during which several additions of lauroylperoxide are made:

8.6 mg after 2 hours,

8.5 mg after 4 hours.

The traces of residual vinyl acetate are removed by evaporation underhigh vacuum. The results are given in Table 12.

Example 3.7 p(EtA-b-tBuA) Block Copolymer

The following are introduced into a round-bottomed flask:

1.881 g of ethyl acrylate,

0.111 g of ethyl α-(O-ethylxanthyl)propionate and

9.0 mg of lauroyl peroxide. The temperature is raised to 80° C. Thepolymerization lasts 6 hours, during which several additions of lauroylperoxide are made:

8.6 mg after 2 hours,

8.9 mg after 4 hours.

After cooling, the traces of residual ethyl acrylate are removed byevaporation under high vacuum and a small fraction of the polymer istaken to be analysed by GPC in THF medium and in polystyreneequivalents:

degree of conversion: 98.6%

M_(n) =2600

PI=1.9.

Next, the following are introduced into the flask:

2.7467 g of tert-butyl acrylate and

8.5 mg of lauroyl peroxide.

The temperature is raised to 80° C. The polymerization lasts 6 hours,during which several additions of lauroyl peroxide are made:

8.7 mg after 2 hours,

8.5 mg after 4 hours.

The traces of residual tert-butyl acrylate are removed by evaporationunder high vacuum and the copolymer obtained is analysed by GPC in THFmedium and in polystyrene equivalents. The results are given in Table12.

Example 3.8 p(t-BuA-b-VA) Block Copolymer

The following are introduced into a round-bottomed flask:

2.737 g of tert-butyl acrylate,

0.111 g of ethyl α-(O-ethylxanthyl)propionate and

8.7 mg of lauroyl peroxide.

The temperature is raised to 80° C. The polymerization lasts 6 hours,during which several additions of lauroyl peroxide are made:

8.9 mg after 2 hours,

8.9 mg after 4 hours.

After cooling, the residual traces of tert-butyl acrylate are removed byevaporation under high vacuum and a small fraction of the polymer istaken to be analysed by GPC in THF medium and in polystyreneequivalents:

degree of conversion: 98.3%,

M_(n) =2500,

PI=2.4.

Next, the following are introduced into the flask:

1.851 g of vinyl acetate and

8.5 mg of lauroyl peroxide.

The temperature is raised to 80° C. The polymerization lasts 6 hours,during which several additions of lauroyl peroxide are made:

8.7 mg after 2 hours,

8.5 mg after 4 hours.

The traces of residual vinyl acetate are removed by evaporation underhigh vacuum and the copolymer obtained is analysed by GPC in THF mediumand in polystyrene equivalents. The results are given in Table 12.

Example 3.9 p(tBuA-b-EtA) Block Copolymer

The following are introduced into a round-bottomed flask:

2.737 g of tert-butyl acrylate,

0.111 g of ethyl α-(O-ethylxanthyl)propionate and

8.4 mg of lauroyl peroxide.

The temperature is raised to 80° C. The polymerization lasts 6 hours,during which several additions of lauroyl peroxide are made:

9.0 mg after 2 hours,

8.7 mg after 4 hours.

After cooling, the residual traces of tert-butyl acrylate are removed byevaporation under high vacuum and a small fraction of the polymer istaken to be analysed by GPC in THF medium and in polystyreneequivalents:

degree of conversion: 98.1%,

M_(n) =2500,

PI=2.5.

Next, the following are introduced into the flask:

1.896 g of ethyl acrylate and

8.8 mg of lauroyl peroxide.

The temperature is raised to 80° C. The polymerization lasts 6 hours,during which several additions of lauroyl peroxide are made:

8.7 mg after 2 hours,

8.5 mg after 4 hours.

The traces of residual ethyl acrylate are removed by evaporation underhigh vacuum and the copolymer obtained is analysed by GPC in THF mediumand in polystyrene equivalents. The results are given in Table 12.

Example 3.10 p(EtA-b-St) Block Copolymer

The following are introduced into a round-bottomed flask:

1.881 g of ethyl acrylate,

0.111 g of ethyl α-(O-ethylxanthyl)propionate and

8.8 mg of lauroyl peroxide.

The temperature is raised to 80° C. The polymerization lasts 6 hours,during which several additions of lauroyl peroxide are made:

9.0 mg after 2 hours,

8.5 mg after 4 hours.

After cooling, the residual traces of ethyl acrylate are removed byevaporation under high vacuum and a small fraction of the polymer istaken to be analysed by GPC in THF medium and in polystyreneequivalents:

degree of conversion: 97.5%,

M_(n) =3000,

PI=1.8.

Next, the following are introduced into the flask:

2.231 g of styrene and

9.0 mg of lauroyl peroxide.

The temperature is raised to 115° C. The polymerization lasts 6 hours,during which several additions of lauroyl peroxide are made:

8.7 mg after 2 hours,

9.9 mg after 4 hours.

The traces of residual styrene are removed by evaporation under highvacuum and the copolymer obtained is analysed by GPC in THF medium andin polystyrene equivalents. The results are given in Table 12.

Example 3.11 p(tBuA-b-St) Block Copolymer

The following are introduced into a round-bottomed flask:

2.737 g of tert-butyl acrylate,

0.111 g of ethyl α-(O-ethylxanthyl)propionate and

9.0 mg of lauroyl peroxide.

The temperature is raised to 80° C. The polymerization lasts 6 hours,during which several additions of lauroyl peroxide are made:

8.5 mg after 2 hours,

9.6 mg after 4 hours.

After cooling, the residual traces of tert-butyl acrylate are removed byevaporation under high vacuum and a small fraction of the polymer istaken to be analysed by GPC in THF medium and in polystyreneequivalents:

degree of conversion: 98.4%,

M_(n) =2800,

PI=2.4.

Next, the following are introduced into the flask:

2.246 g of styrene and

8.4 mg of lauroyl peroxide.

The temperature is raised to 115° C. The polymerization lasts 6 hours,during which several additions of lauroyl peroxide are made:

9.2 mg after 2 hours,

9.2 mg after 4 hours.

The traces of residual styrene are removed by evaporation under highvacuum and the copolymer obtained is analysed by GPC in THF medium andin polystyrene equivalents. The results are given in Table 12.

Example 3.12 p(EtA-b-tBuA-b-St) Block Copolymer

The following are introduced into a round-bottomed flask:

2.248 g of styrene,

the entire copolymer obtained in Example 3.7 and

8.3 mg of lauroyl peroxide.

The temperature is raised to 115° C. The polymerization lasts 6 hours,during which several additions of lauroyl peroxide are made:

9.0 mg after 2 hours,

8.5 mg after 4 hours.

The traces of residual styrene are removed by evaporation under highvacuum and the copolymer obtained is analysed by GPC in THF medium andin polystyrene equivalents. The results are given in Table 12.

Example 3.13 p(St-b-EtA) Block Copolymer

The following are introduced into a round-bottomed flask:

2.224 g of styrene,

0.111 g of ethyl α-(O-ethylxanthyl)propionate and

8.6 mg of lauroyl peroxide.

The temperature is raised to 115° C. The polymerization lasts 6 hours,during which several additions of lauroyl peroxide are made:

8.7 mg after 2 hours,

8.3 mg after 4 hours.

After cooling, the traces of residual styrene are removed by evaporationunder high vacuum and a small fraction of the polymer is taken to beanalysed by GPC in THF medium and in polystyrene equivalents:

degree of conversion: 98.0%

M_(n) =3500,

PI=2.2.

Next, the following are introduced into the flask:

2 ml of toluene,

1.892 ? of ethyl acrylate and

8.5 mg of lauroyl peroxide.

The temperature is raised to 80° C. The polymerization lasts 6 hours,during which several additions of lauroyl peroxide are made:

9.4 mg after 2 hours,

9.2 mg after 4 hours.

The traces of residual ethyl acrylate are removed by evaporation underhigh vacuum and the copolymer obtained is analysed by GPC in THF mediumand in polystyrene equivalents. The results are given in table 12.

Example 3.14 p(St-b-tBuA) Block Copolymer

The following are introduced into a round-bottomed flask:

2.224 g of styrene,

0.111 g of ethyl α-(O-ethylxanthyl)propionate and

8.6 mg of lauroyl peroxide.

The temperature is raised to 115° C. The polymerization lasts 6 hours,during which several additions of lauroyl peroxide are made:

8.7 mg after 2 hours,

9.5 mg after 4 hours.

After cooling, the traces of residual styrene are removed by evaporationunder high vacuum and a small fraction of the polymer is taken to beanalysed by GPC in THF medium and in polystyrene equivalents:

degree of conversion: 97.2%

M_(n) =3400,

PI=2.2.

Next, the following are introduced into the flask:

2 ml of toluene,

2.747 g of tert-butyl acrylate and

9.3 mg of lauroyl peroxide.

The temperature is raised to 80° C. The polymerization lasts 6 hours,during which several additions of lauroyl peroxide are made:

8.7 mg after 2 hours,

9.3 mg after 4 hours.

The traces of residual tert-butyl acrylate are removed by evaporationunder high vacuum and the copolymer obtained is analysed by GPC in THFmedium and in polystyrene equivalents. The results are given in table12.

Example 3.15 p(tBuA-b-EtA-b-St) Block Copolymer

The following are introduced into a round-bottomed flask:

2 ml of toluene,

2.229 g of styrene,

the entire copolymer obtained in Example 3.9 and

9.1 mg of lauroyl peroxide.

The temperature is raised to 120° C. The polymerization lasts 6 hours,during which several additions of lauroyl peroxide are made:

8.5 mg after 2 hours,

8.5 mg after 4 hours.

The traces of residual styrene are removed by evaporation under highvacuum and the copolymer obtained is analysed by GPC in THF medium andin polystyrene equivalents. The results are given in Table 12.

Example 3.16 p(BuA-b-PVA) Block Copolymers

(PVA: polyvinyl alcohol)

These copolymers are obtained by hydrolysing their p(BuA-b-VA)equivalents.

A series of p(BuA-b-VA) block copolymers is prepared. All the copolymersare obtained according to the following general operating method.

The following are introduced into a round-bottomed flask:

butyl acrylate (BuA),

ethyl α-(O-ethylxanthyl)propionate and

approximately one third of the total amount of lauroyl peroxidenecessary for this first step.

The temperature is raised to 80° C. The polymerization lasts 6 hours,during which two additions of initiator are made after 2 and 4 hours.Each of the additions corresponds to approximately one third of thetotal amount of lauroyl peroxide of the first step.

The traces of residual butyl acrylate are removed by evaporation and asmall fraction of the polymer is taken to be analysed.

Next, the following are added to the flask:

vinyl acetate and

approximately one third of the total amount of lauroyl peroxidenecessary for this second step.

The temperature is again raised to 80° C. The polymerization lasts 6hours and the rest of the initiator is added in the same way as for thesynthesis of the first block. The block copolymer is recovered afterevaporating the traces of residual vinyl acetate and analysed by GPC inTHF medium and in polystyrene equivalents.

The amounts of ingredients used for each of the copolymers, as well asthe results obtained, are given in Table 11.

                  TABLE 11                                                        ______________________________________                                                       Homo-    Polymerization                                                                            Block                                     Polymerization 1                                                                             polymer  2           polymer                                   BuA   Precursor                                                                              Perox.           VA    Perox.                                  mass  mass     mass             mass  mass                                    (g)   (g)      (mg)    M.sub.n                                                                            PI  (g)   (mg)  M.sub.n                                                                            PI                           ______________________________________                                        13.713                                                                              1.126    0.257   2500 1.6 13.789                                                                              0.263 4500 1.4                          13.695                                                                              1.125    0.257   2500 1.6 18.395                                                                              0.265 5300 1.4                          19.158                                                                              0.791    0.347   3900 2.0 6.461 0.350 5600 1.7                          19.157                                                                              0.798    0.360   3900 2.0 12.872                                                                              0.352 7200 1.6                          19.242                                                                              1.568    0.370   2500 1.6 6.470 0.365 3200 1.5                          19.295                                                                              1.568    0.371   2500 1.7 12.969                                                                              0.359 4100 1.4                          6.71  1.067    0.246   1500 1.4 22.027                                                                              0.497 5900 1.5                          ______________________________________                                    

Next, the block polymers obtained are hydrolysed: they are dissolved inmethanol, with 50% solids content, and then a catalytic amount of sodiumhydroxide is added and the reaction mixture is heated at 60° C. for 1hour.

The p(BuA-b-PVA) copolymers are recovered by evaporating the methanol.

Example 3.17 p(AA-b-PVA) Block Copolymer

This copolymer is obtained by hydrolysing the corresponding p(tBuA-b-VA)copolymer.

The following are introduced into a round-bottomed flask:

2.737 g of tert-butyl acrylate,

0.111 g of ethyl α-(O-ethylxanthyl)propionate and

8.5 mg of lauroyl peroxide.

The temperature is raised to 80° C.

The polymerization lasts 6 hours, during which several additions oflauroyl peroxide are made:

9.5 mg after 2 hours,

9.8 mg after 4 hours.

After cooling, the traces of residual tert-butyl acrylate are removed byevaporation under high vacuum.

A small fraction of the polymer is taken to be analysed by GPC in THFmedium and in polystyrene equivalents:

degree of conversion: 99.0%,

M_(n) =4300,

PI=1.7.

Next, the following are introduced into the flask:

1.831 g of vinyl acetate and

8.6 mg of lauroyl peroxide.

The temperature is raised to 80° C.

The polymerization lasts 6 hours, during which several additions oflauroyl peroxide are made:

9.2 mg after 2 hours,

9.2 mg after 4 hours.

The traces of residual vinyl acetate are removed by evaporation underhigh vacuum and the copolymer obtained is analysed by GPC in THF mediumand in polystyrene equivalents. The results are given in Table 12.

Next, the copolymer obtained is hydrolysed in the following manner.

The copolymer is introduced into a water/methanol (10 ml/4 ml) mixture.Three drops of 95% sulphuric acid are added so as to obtain a pH of 1.The temperature is raised to 70° C. After 2 hours 15 minutes, 8 ml ofmethanol are added and, after 5 hours, three new drops of 95% sulphuricacid are added. This first step lasts 24 hours and enables thepoly(tert-butyl acrylate) block to be converted into polyacrylic acid.

Next, the temperature is returned to room temperature and the solvent(water+methanol) is removed by evaporation. The dry residue obtained isredissolved in 30 ml of methanol and a catalytic amount of NaOH isadded. The temperature is again raised to 70° C., at which it ismaintained for 24 hours.

The polyacrylic acid/polyvinyl alcohol copolymer obtained is recoveredby evaporating the methanol.

Example 3.18 p(BuA-b-EtA) Block Copolymer

The following are introduced into a reactor fitted with a stirringsystem:

60 g of isopropyl acetate,

90 g of butyl acrylate and

6.9 g of ethyl α-(O-ethylxanthyl)propionate.

The temperature is raised to 80° C. 0.18 g of AIBN in solution in 5 g ofisopropyl acetate are added in one go.

Fifteen minutes later, a solution containing:

180 g of isopropyl acetate,

274 g of butyl acrylate and

0.5 g of AIBN

is fed continuously over a period of 2 hours.

The temperature and stirring are maintained for 1 hour 45 minutes afterthe end of adding the first monomer.

A small fraction of the precursor polymer is taken and analysed by GPCin THF medium and in polystyrene equivalents:

M_(n) =7000,

PI=1.9.

A second continuous feed then takes place over a period of 1 hour. Itconsists of a solution containing:

10 g of isopropyl acetate,

163 g of ethyl acrylate and

0.32 g of AIBN.

The temperature and stirring are maintained for one further hour afterthe end of adding the second monomer.

The final copolymer is obtained by evaporating the solvent and thetraces of residual monomers and is analysed by GPC in THF medium and inpolystyrene equivalents. The results are given in Table 12.

Example 3.19 p(BuA-b-EtA) Block Copolymer

The following are introduced into a reactor fitted with a stirringsystem:

45 g of isopropyl acetate,

75 g of butyl acrylate and

6.9 g of ethyl α-(O-ethylxanthyl)propionate.

The temperature is raised to 80° C. and 0.15 g of AIBN in solution in 5g of isopropyl acetate are added in one go.

Twenty minutes later, a solution containing:

117 g of isopropyl acetate,

175 g of butyl acrylate and

0.35 g of AIBN

is fed continuously over a period of 1 hour 30 minutes.

The temperature and stirring are maintained for 2 hours 10 minutes afterthe end of adding the first monomer.

A small fraction of the precursor polymer is taken and analysed by GPCin THF medium and in polystyrene equivalents:

M_(n) =5200

PI=1.8.

A second continuous feed is then carried out over a period of 1 hour 40minutes. It consists of a solution containing:

168 g of isopropyl acetate,

252 g of ethyl acrylate and

0.5 g of AIBN.

The temperature and stirring are maintained for a further 20 minutesafter the end of adding the second monomer.

The final copolymer is recovered by evaporating the solvent and thetraces of residual monomers and is analysed by GPC in THF medium and inpolystyrene equivalents. The results are given in Table 12.

Results of Examples 3.1 to 3.19

                  TABLE 12                                                        ______________________________________                                        Monomers                       Degree of                                      Examples                                                                              M1     M2       M3   M.sub.n PI  conversion                           ______________________________________                                        Ex. 3.1 MeA    St       --   4650    1.6                                      Ex. 3.2 St     MeA      --   4300    1.7                                      Ex. 3.3 St     MeA      --   4200    1.8                                      Ex. 3.4 St     MeA      St   6200    2                                        Ex. 3.5 MeA    St       --   3750    1.8                                      Ex. 3.6 EtA    VA       --   5600    1.4 92.3%                                Ex. 3.7 EtA    tBuA     --   6800    1.7 97.8%                                Ex. 3.8 tBuA   VA       --   6900    1.5 83.8%                                Ex. 3.9 tBuA   EtA      --   7000    2.0 96.1%                                Ex. 3.10                                                                              EtA    St       --   7600    1.8 98.4%                                Ex. 3.11                                                                              tBuA   St       --   8100    2.9 95.9%                                Ex. 3.12                                                                              EtA    tBuA     St   13,000  2.4 97.5%                                Ex. 3.13                                                                              St     EtA      --   6200    1.9 >99%                                 Ex. 3.14                                                                              St     tBuA     --   7100    1.9 >99%                                 Ex. 3.15                                                                              tBuA   EtA      St   11,400  2.4 >99%                                 Ex. 3.17                                                                              tBuA   VA       --   7400    1.4 88%                                  Ex. 3.18                                                                              BuA    EtA      --   8700    2.2 95%                                  Ex. 3.19                                                                              Bua    EtA      --   10,000  2.0 80%                                  ______________________________________                                    

What is claimed is:
 1. A process for preparing block polymers of generalformula (I): ##STR17## wherein: Z¹ =S or P,Z² =O, S or P, R¹ and R²,which are identical or different, represent:an alkyl, acyl, aryl, alkeneor alkyne group (i), an saturated or unsaturated, carbon-containing oraromatic ring (ii), an saturated or unsaturated heterocycle (iii), V,V', W and W', which are identical or different, represent H, an alkylgroup or a halogen, X, X', Y and Y', which are identical or different,represent H, a halogen, R³, OR³, O₂ COR³, NHCOH, OH, NH₂, NHR³, N(R³)₂,(R³)₂ N⁺ O⁻, NHCOR³, CO₂ H, CO₂ R³, CN, CONH₂, CONHR³ or CONR³ ₂ group,wherein R³ is alkyl, aryl, aralkyl, alkaryl, alkene or organo-silylgroups, optionally perfluorinated, a and b, which are identical ordifferent, are equal to 0 or 1, m and n, which are identical ordifferent, are greater than or equal to 1 and, when one or other isgreater than 1, the individual repeat units are identical ordifferent,said process comprising the step of bringing into contact witheach other: an ethylenically unsaturated monomer of formula:CYY'(═CW--CW')_(a) ═CH₂, a precursor compound of general formula (II):##STR18## and a radical polymerization initiator.
 2. A process accordingto claim 1, wherein said hydrophilic or ionic group is an alkali metalsalt of carboxylic acids, an alkali metal salt of sulphonic acid, apolyethylene oxide chain, a polypropylene oxide chain, a cationicsubstituent, or a quaternary ammonium salt.
 3. A process according toclaim 1, wherein the ethylenically unsaturated monomer is styrene, astyrene derivative, butadiene, chloroprene, acrylic ester, methacrylicester or a vinylnitrile.
 4. A process according to claim 3, wherein theethylenically unsaturated monomer is vinylacetate, vinylversatate, orvinylpropionate.
 5. A process according to claim 1, wherein R¹represents:a group of formula CR'¹ R'² R'³, wherein R'¹, R'² and R'³represent groups (i), (ii) or (iii), or a --COR'⁴ group, wherein R'⁴represents a group (i), (ii) or (iii).
 6. A process according to claim1, wherein R¹ represents:a group of formula CR'¹ R'² R'³, wherein R'¹=R'² =H and R'³ is an aryl, alkene or alkyne group, or a --COR'⁴ group,wherein R'⁴ represents a group (i), (ii) or (iii).
 7. A processaccording to claim 1, wherein R² represents a group of formula: --CH₂R'⁵, in which R'⁵ represents H or a group (i), (ii) or (iii) with theproviso that R'⁵ is not an aryl group, an alkyne group, or an alkenegroup.
 8. A process according to claim 1, wherein Z¹ is a sulphur atomand Z² is an oxygen atom.
 9. A process according to claim 8, wherein:R¹is: ##STR19## and R² is an ethyl or phenyl group.
 10. A processaccording to claim 1, wherein the compounds (II) are styrene, methylacrylate, ethyl acrylate, butyl acrylate, tert-butyl acrylate, vinylacetate, and an acrylic acid homopolymer, wherein:Z¹ =S, Z² =O, R¹=CHCH₃ (CO₂ Et) and R² =Et, or Z¹ =S, Z² =O, R¹ =CH(CO₂ Et)₂ and R² =Et.11. A process according to claim 1, wherein the precursor compound ofgeneral formula (II) is a polymer and wherein said polymer is made byradical polymerization of an ethylenically unsaturated monomer offormula: CXX'(═CV--CV')_(b) ═CH₂, comprising the step of bringing intocontact said monomer with a radical polymerization initiator and acompound of general formula (III), (IV) or (V): ##STR20## wherein p isbetween 2 and
 10. 12. A process according to claim 11, wherein thecompound (III) is ethyl-α-(O-ethylxanthyl)propionate or ethyl(O-ethylxanthyl)malonate.
 13. A process for preparing block polymers,comprising the steps of:a) preparing a block polymer of general formula(I): ##STR21## wherein: Z¹ =S or P,Z² =O, S or P, R¹ and R², which areidentical or different, represent:an alkyl, acyl, aryl, alkene or alkynegroup (i), a saturated or unsaturated, carbon-containing or aromaticring (ii), a saturated or unsaturated heterocycle (iii), V, V', W andW', which are identical or different, represent H, an alkyl group or ahalogen, X, X', Y and Y', which are identical or different, represent H,a halogen, R³, OR³, O₂ COR³, NHCOH, OH, NH₂, NHR³, N(R³)₂, (R³)₂ N⁺ O⁻,NHCOR³, CO₂ H, CO₂ R³, CN, CONH₂, CONHR³ or CONR³ ₂ group, wherein R³ isalkyl, aryl, aralkyl, alkaryl, alkene or organo-silyl groups, optionallyperfluorinated a and b, which are identical or different, are equal to 0or 1, m and n, which are identical or different, are greater than orequal to 1 and, when one or other is greater than 1, the individualrepeat units are identical or different, said process comprising thestep of bringing into contact with each other: an ethylenicallyunsaturated monomer of formula: CYY'(═CW--CW')_(a) ═CH₂, a precursorcompound of general formula (II): ##STR22## and a radical polymerizationinitiator, b) repeating at least one more time step a) except thatdifferent monomers from those used in step a) are used, and using,instead of the precursor compound of formula (II), the block polymerobtained in step a).
 14. A process according to claim 13, wherein theblock polymer so obtained has a polydispersity index of at most
 2. 15. Aprocess according to claim 14, wherein the block polymer has apolydispersity index of at most 1.5.
 16. A process according to claim13, wherein the block polymer is of general formula (I) wherein Z¹ is asulphur atom and Z² is an oxygen atom.
 17. A process according to claim13, wherein the block polymer has at least two polymer blocks selectedfrom the group consisting ofpolystyrene/polymethyl acrylate,polystyrene/polyethyl acrylate, polystyrene/poly(tert-butyl acrylate),polyethyl acrylate/polyvinyl acetate, polybutyl acrylate/polyvinylacetate, polyethyl acrylate/poly(tert-butyl acrylate), poly(tert-butylacrylate)/polyvinyl acetate, polyethyl acrylate/polybutyl acrylate,polybutyl acrylate/polyvinyl alcohol, and polyacrylic acid/polyvinylalcohol.
 18. A process according to claim 1, wherein the block polymerso obtained has a polydispersity index of at most
 2. 19. A processaccording to claim 18, wherein the block polymer has a polydispersityindex of at most 1.5.
 20. A process according to claim 1, wherein theblock polymer is of general formula (I) wherein Z¹ is a sulphur atom andZ² is an oxygen atom.
 21. A process according to claim 1, wherein theblock polymer has at least two polymer blocks selected from the groupconsisting ofpolystyrene/polymethyl acrylate, polystyrene/polyethylacrylate, polystyrene/poly(tert-butyl acrylate), polyethylacrylate/polyvinyl acetate, polybutyl acrylate/polyvinyl acetate,polyethyl acrylate/poly(tert-butyl acrylate), poly(tert-butylacrylate)/polyvinyl acetate, polyethyl acrylate/polybutyl acrylate,polybutyl acrylate/polyvinyl alcohol, and polyacrylic acid/polyvinylalcohol.
 22. A process according to claim 11, wherein the block polymerso obtained has a polydispersity index of at most
 2. 23. A processaccording to claim 22, wherein the block polymer has a polydispersityindex of at most 1.5.
 24. A process according to claim 11, wherein theblock polymer is of general formula (I) wherein Z¹ is a sulphur atom andZ² is an oxygen atom, and n is greater or equal to
 6. 25. A processaccording to claim 11, wherein the block polymer is of general formula(I), wherein:Z¹ =S, Z² =O, R¹ =CHCH₃ (CO₂ Et) and R² =Et, or Z¹ =S, Z²=O, R¹ =CH(CO₂ Et)₂ and R² =Et.
 26. A process according to claim 11,wherein the block polymer of general formula (I), is styrene, methylacrylate, ethyl acrylate, butyl acrylate, tert-butyl acrylate, vinylacetate, and acrylic acid polymers, wherein:Z¹ =S, Z² =O, R¹ =CHCH₃ (CO₂Et) and R² =Et, or Z¹ =S, Z² =O, R¹ =CH(CO₂ Et)₂ and R² =Et.
 27. Aprocess according to claim 1, wherein the group (i), ring (ii) andheterocycle (iii) are further substituted with a substituted phenyl,substituted aromatic, alkoxycarbonyl, aryloxycarbonyl (--COOR), carboxy(--COOH), acyloxy (--O₂ CR), carbamoyl (--CONR₂), cyano (--CN),alkylcarbonyl, alkylarylcarbonyl, arylcarbonyl, arylalkylcarbonyl,phthalimido, maleimido, succinimido, amidino, guanidimo, hydroxyl(--OH), amino (--NR₂), halogen, allyl, epoxy, alkoxy (--OR), S-alkyl,S-aryl, a hydrophilic group or ionic group, wherein R represents analkyl group, an aryl group, or a polymer chain.
 28. A process accordingto claim 13, wherein the group (i), ring (ii) and heterocycle (iii) arefurther substituted with a substituted phenyl, substituted aromatic,alkoxycarbonyl, aryloxycarbonyl (--COOR), carboxy (--COOH), acyloxy(--O₂ CR), carbamoyl (--CONR₂), cyano (--CN), alkylcarbonyl,alkylarylcarbonyl, arylcarbonyl, arylalkylcarbonyl, phthalimido,maleimido, succinimido, amidino, guanidimo, hydroxyl (--OH), amino(--NR₂), halogen, allyl, epoxy, alkoxy (--OR), S-alkyl, S-aryl, ahydrophilic group or ionic group, wherein R represents an alkyl group,an aryl group, or a polymer chain.
 29. A process according to claim 1,wherein R3 is substituted with one or more groups selected from thegroup consisting of carboxyl, epoxy, hydroxyl, alkoxy, amino, halogenand sulphonic groups.
 30. A process according to claim 13, wherein R3 issubstituted with one or more groups selected from the group consistingof carboxyl, epoxy, hydroxyl, alkoxy, amino, halogen and sulphonicgroups.